From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with ESMTP id BAFBB6B01AC for ; Wed, 2 Jun 2010 02:17:18 -0400 (EDT) Date: Tue, 1 Jun 2010 23:16:00 -0700 From: Andrew Morton Subject: Re: [PATCH] hugetlb: call mmu notifiers on hugepage cow Message-Id: <20100601231600.3b3bf499.akpm@linux-foundation.org> In-Reply-To: <4BFED954.8060807@cray.com> References: <4BFED954.8060807@cray.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Doug Doan Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, andi@firstfloor.org, lee.schermerhorn@hp.com, rientjes@google.com, mel@csn.ul.ie, Andrea Arcangeli List-ID: On Thu, 27 May 2010 13:43:00 -0700 Doug Doan wrote: > > When a copy-on-write occurs, we take one of two paths in handle_mm_fault: > through handle_pte_fault for normal pages, or through hugetlb_fault for huge pages. > > In the normal page case, we eventually get to do_wp_page and call mmu notifiers > via ptep_clear_flush_notify. There is no callout to the mmmu notifiers in the > huge page case. This patch fixes that. > > Signed-off-by: Doug Doan > --- > > [patch text/plain (802B)] > --- mm/hugetlb.c.orig 2010-05-27 13:07:58.569546314 -0700 > +++ mm/hugetlb.c 2010-05-26 14:41:06.449296524 -0700 (In patch -p1 form, please. So a/mm/hugetlb.c) > @@ -2345,11 +2345,17 @@ retry_avoidcopy: > ptep = huge_pte_offset(mm, address & huge_page_mask(h)); > if (likely(pte_same(huge_ptep_get(ptep), pte))) { > /* Break COW */ > + mmu_notifier_invalidate_range_start(mm, > + address & huge_page_mask(h), > + (address & huge_page_mask(h)) + huge_page_size(h)); > huge_ptep_clear_flush(vma, address, ptep); > set_huge_pte_at(mm, address, ptep, > make_huge_pte(vma, new_page, 1)); > /* Make the old page be freed below */ > new_page = old_page; > + mmu_notifier_invalidate_range_end(mm, > + address & huge_page_mask(h), > + (address & huge_page_mask(h)) + huge_page_size(h)); > } > page_cache_release(new_page); > page_cache_release(old_page); This causes mmu_notifier_invalidate_range_start() to be called under page_table_lock. The immediately preceding code seems to take some care to avoid doing that. I took a quick look at other callsites and cannot immediately see other cases where mmu_notifier_invalidate_range_start/end() are called under that lock. This may not introduce bugs with current notifier implementations (I didn't check), but it does lessen flexibility? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org